The effects of ultrasound at typical diagnostic doses on the different parameters of the immune response to infection with vaccinia virus will be evaluated using a well characterized hamster model. In vitro assays of immunity will be used to test for ultrasound-induced immunosuppression (or stimulation) of the three major components of the immune response to vaccinia, i.e., antibody response, T-lymphocyte response, and macrophage response. The effects of ultrasound on the activities of two naturally occurring immune mechanisms, NK cells and K cells, will also be evaluated. In addition to scanned abdominally ultrasonic irradiation, animals will be treated with localized (spleen) irradiation and lymphoid cells will be exposed in vitro to ultrasound to further define the targets of the potential immunological effects of this type of irradiation. Recently, researchers have reported evidence suggesting that ultrasound at diagnostic levels may cause immunosuppressive and other immune system changes. Since the clinical use of ultrasound is increasing significantly, it is of considerable importance that exposure levels which produce effects be established with precision so that potential risks can be adequately assessed. In this proposed research, we will determine quantitative relationships between threshold and suprathreshold exposure parameters and observed immunological changes.